1. Field of the Invention
The present invention is related to reactive inorganic clusters with reactive functionalities, such as amino groups; and a process for preparing such reactive clusters. The clusters may be used as curing agents for thermosetting resins.
2. Description of Background and Related Art
Silicon-containing materials produced by prior art methods are known to be useful as fillers in various compositions. For example, in some applications, it is desired to incorporate silica structures into a resin matrix, such as a thermosetting resin, by chemically reacting the silica structures with the resin to provide organic-inorganic hybrid materials in order to improve the thermo-mechanical properties of the resin. For example, thermosetting resins, such as epoxy resins, are typically used in the field of electrical and electronic materials; and for these applications materials with improved heat resistance (e.g. glass transition temperature greater than 120° C., decomposition temperature measured at 5% weight loss greater than 300° C.) and low coefficient of linear expansion (CTE) (e.g., less than 60 ppm/K at 25° C.) are required. It is known that incorporating silica structures into an epoxy matrix can lead to improved thermo-mechanical properties.
It is also well known to produce silicon-containing materials by various processes. Then, as aforementioned, these pre-formed silica structures may be used, for example, as fillers or additives in various compositions. In addition to processes that produce typical pre-formed non-reactive silica fillers, there is a known process, commonly referred to as a “sol-gel in-situ process,” that can be used to produce reactive silica systems.
There are several routes which use a sol-gel process to prepare an organic/inorganic hybrid material for thermosetting resins such as epoxy resins. For example, in general, a first route related to known sol-gel processes, involves preparing a silicon-modified epoxy resin containing hydrolysable alkoxysilane groups, which condense during reaction with water. Then the resulting system is cured with a conventional hardener at an elevated temperature.
A second route consists of first preparing a partial condensate of an alkoxysilane, which in turn, is mixed with an epoxy resin. The resulting system is then cured with a hardener at an elevated temperature.
A third route involves preparing an organic/inorganic hybrid material consisting of physically mixing monomeric alkoxysilanes into an epoxy composition.
A problem associated with sol-gel processes reported in the prior art relates to the use of an organic solvent which must eventually be removed from the final product. Another common problem associated with the sol-gel process is the relatively high amount (e.g. greater than 10% by weight) of volatile by-products (e.g., alcohol and water) generated during the sol-gel process. Because of these two limitations associated with the sol-gel process, only thin materials (membranes and protective coatings) have previously been developed while bulk materials have not been described in the prior art. The limitations of the known sol-gel processes makes it very difficult to prepare bulk materials in the industry.
In comparison with classical pre-formed silica fillers, sol-gel in-situ formed silica allows for the production of a reactive system with a low viscosity (e.g., less than 100 Pa·s at 25° C.) enabling better processing. However, as aforementioned, recurring problems associated with a sol-gel process include the added burden of having to remove any organic solvents, used in the process, from the final product; and the relatively high amount of volatile by-products generated during the sol-gel process.
It is therefore desirable to provide a process which enables the preparation of inorganic structures, in particular silicon-containing structures, which can be prepared more readily and more economical without the problems of the prior art processes such as without the addition of a solvent at any stage of the preparation. In addition, it is desired to provide a silica structure than can be useful for reacting into a thermosetting resin, such as an epoxy resin matrix, to provide an organic-inorganic hybrid material with improved properties.